Problem with low virtual memory

I was buying a computer the other day. I install the things that was needed in the computer. Though my computer had only40Gb and 256 RAM, its functioning well. As I install the Antivira antivirus I have problem. It stated that my virtual memory is low....so I searched the net what is it...! I tried to change the capacity but it was no use. So I just believe in my own self capability. As I run the task manager or simply control + alt+ delete, I started ending the process of some programs there which I rarely use. I just delete the programs that the users used not the SYSTEM. There and I got it. My computer got work so well and I get my self-esteem high.